“Stress changes the way we process food,” Jan Kiecolt-Glaser, the study’s lead author and professor of psychiatry and psychology at Ohio State University told The Huffington Post.

Her team found that when women ate a high calorie breakfast loaded with ‘healthy’ fat after a stressful event, their bodies not only burned fewer calories, they also showed raised levels of harmful health indicators in their blood ― just the same as if they had eaten the meal with ‘bad’ fat.

For the study, Kiecolt-Glaser and team compared women who ate identical breakfasts of biscuits, gravy, eggs and turkey sausage. Some of the meals were made with palm oil, which is high in saturated fat. Others ate the same meal, but prepared it with monounsaturated sunflower oil, which is considered a “good” fat. Both breakfasts contained 930 calories and 60 grams of fat, which is almost the same as eating a Big Mac and medium fries.

When women had a stressful event the day before breakfast ― ranging from cleaning up paint spilled by a child on the floor to caring for a parent with dementia ― the emotional reaction to that event cancelled out the benefits of the healthier fat, the researchers wrote.

The women who ate meals of “bad” fat showed higher blood markers for increased inflammation and the likelihood of plaque build-up in the arteries. It’s understood that “good” fat lowers inflammation, explained Kiecolt-Glaser, but after a stressful event, participants who ate the monounsaturated fat fared the same in blood tests as their counterparts.

It’s important to note that the study, published in Molecular Psychiatry, did not test for the effect of stress on people who ate a balanced or low-calorie diet. It suggests that individuals who eat extremely high fat and high calorie diets burn fewer calories when stressed.

It’s not all about the body when it comes to weight loss efforts and stress can also sabotage healthy behaviors that could support weight loss.

“Stress makes it hard to lose weight,” Kiecolt-Glaser said. “Several things are happening: we eat comfort food, we’re sleeping more poorly and we’re hungrier the next day. And when we’re stressed we’re less likely to exercise.”

While we don’t have all the answers, this study is worth keeping in mind if you are making an effort to load up on healthy fats. Good fat, bad fat? It might only matter if you chill out.